With the development of integrated circuit manufacture,it is possible to integrate multispectral linear array infrared detector on one chip. One of the major challenges is parasitic effects in ROIC design for long linear array. This paper analysed an ROIC design for multispectral long linear array which encountered obvious difference for ultra-small integrate capacitor between consecutive line output while the input unchanged,which results in bright-dark line in an image. Thorough testing and analyzing,the cause was found due to the parasitic effects of the complicated circuit layout. A more robust layout design was taped out and the problem was resolved.